Theories of Development.
Lamarck.
Lamarck, a distinguished French naturalist, was the first of modern scientific men who adopted the theory that all vegetables and animals living on the earth, including man, are developed from certain original, simple germs. This doctrine was expounded in his *' Zoologie Philosophique," published in 1809. Lamarck admitted the existence of God, to whom he referred the existence of the matter of which the universe is composed. But God having cre- ated matter Avith its properties, does nothing more. Life, organ- isms, and mind are all the product of unintelligent matter and its forces. All living matter is composed of cellular tissue, consisting of the aggregation of minute cells. These cells are not living in themselves, but are quickened into life by some ethereal fluid per- vading space, such as heat and electricity. Life, therefore, accord- ing to this theory, originates in spontaneous generation.
Life, living cells or tissues, having thus originated, all the diver- sified forms of the vegetable and animal kingdoms have been pro- duced by the operation of natural causes ; the higher, even the highest, being formed from the lowest by a long-continued pro- cess of development.
The principles of Lamarck's theory " are involved in the three following propositions : —
" 1. That any considerable and permanent change in the circum- stances in which a race of animals is placed, superinduces in them a real change in their wants and requirements.
" 2. That this change in their wants necessitates new actions on their part to satisfy those wants, and that finally new habits are thus engendered.
" 3. That these new actions and habits necessitate a greater and more frequent use of particular organs already existing, which thus become strengthened and improved ; or the development of new organs when new wants require them ; or the neglect of the use of old organs, which may thus gradually decrease and finally dis appear." ^
Vestiges of Creation.
Some thirty years since a work appeared anonymously, entitled " The Vestiges of Creation," in which the theory of Lamarck in its essential features was reproduced. The writer agreed with his
1 William Hopkins, F. R. S. Fraser's Magazine, June, 1860, p. 731.
12 PAET n. Ch. l — origin of man.
j)re(lecessor in admitting an original creation of matter ; in referring the origin of life to physical causes ; and in deriving all the genera, species, and varieties of plants and animals by a process of natural development from a common source. These writers differ in the way in which they carry out their common views and as to the grounds which they ixrge in their support.
The author of the " Vestiges of Creation " assumes the truth of the nebular hypothesis, and argues from analogy that as the complicated and ordered systems of the heavenly bodies are the result of physical laws acting on the original matter pervading space, it is reasonable to infer that the different orders of plants and animals have arisen in the same way. He refers to the grada- tion observed in the vegetable and animal kingdoms ; the simpler everywhere preceding the more complex, and the unity of plan being preserved throughout. He lays great stress also on the foetal development of the higher orders of animals. The human foetus, for example, assuming in succession the peculiarities of structure of the reptile, of the fish, of the bird, and of man. This is supposed to prove that man is only a more perfectly developed reptile ; and that the orders of animals differ simply as to the stage they occupy in this unfolding series of life. As the same larva of the bee can be developed into a queen, a drone, or a worker, so the same living cell can be developed into a reptile, a fish, a bird, or a man. There are, however, the author admits, interruptions in the scale ; species suddenly appearing Avithout due preparation. This he illustrates by a reference to the calculating machine, which for a million of times will produce numbers in regular series, and then for once produce a number of a different order ; thus the law of species that like shall beget like may hold good for an indefinite period, and then sud- denly a new species be begotten. These theories and their authors have fallen into utter disrepute among scientific men, and have no other than a slight historical interest.
Darwin.
The new theory on this subject proposed by Mr. Charles Darwin, has, for the time being, a stronger hold on the public mind. He stands in the first rank of naturalists, and is on all sides respected not only for his knowledge and his skill in observation and descrip- tion, but for his frankness and fairness. His theory, however, is substantially the same with those already mentioned, inasmuch as he also accounts for the origin of all the varieties of plants and animals by the gradual operation of natural causes. In his work